public class Text1 {
    // 2.两数相加
    public ListNode addTwoNumbers1(ListNode l1, ListNode l2) {
        ListNode prev = new ListNode(0);

        int carry = 0;
        ListNode cur = prev;
        while(l1!=null||l2!=null){
            int x= l1 !=null ? l1.val : 0;
            int y = l2 !=null ? l2.val : 0;
            int sum = x + y + carry;
            carry = sum/10;
            sum = sum%10;
            cur.next = new ListNode(sum);
            cur = cur.next;

            if(l1 !=null){
                l1 = l1.next;
            }
            if(l2 !=null){
                l2 = l2.next;
            }
        }

        if(carry>0){
            cur.next = new ListNode(1);
        }
        return prev.next;
    }

    // 再刷两数相加
    public ListNode addTwoNumbers2(ListNode l1, ListNode l2) {
        ListNode cur1 = l1, cur2 = l2;
        ListNode newHead =  new  ListNode(0);
        ListNode prev = newHead;
        int t = 0;

        while(cur1 != null || cur2 != null || t != 0){
            if(cur1 != null){
                t += cur1.val;
                cur1 = cur1.next;
            }
            if(cur2 != null){
                t += cur2.val;
                cur2 = cur2.next;
            }

            prev.next = new ListNode(t % 10);
            prev = prev.next;
            t /= 10;
        }

        return newHead.next;
    }
}
